Estuaries—Habitat of the Month

What’s in a Name?

What do you call the place where fresh water meets salt water? It’s an estuary! Estuaries are where fresh water from rivers mixes with salt water from the ocean. These transitional areas that straddle the land and sea contain habitats needed by fish, shellfish, wildlife—and people. Although the word isn’t in their names, Puget Sound, Tampa Bay, Elkhorn Slough, Cook Inlet, and the lower Hudson River are all estuaries.

Often called nurseries of the sea, estuaries provide vital nesting and feeding habitats for many aquatic plants and animals. Most fish and shellfish eaten in the United States, including salmon, herring, and oysters, spend at least part of their life cycles in estuaries. Some, like oysters, make estuaries their permanent home; others, like horseshoe crabs, use them to complete only part of their life cycle.

Economics of Estuaries

Estuaries provide habitat for more than 75 percent of the U.S. commercial fish catch, and an even greater percentage of the recreational fish catch.

The total fish catch in estuaries contributes $4.3 billion a year to the U.S. economy.

Coastal recreation and tourism generate $8-$12 billion per year to the U.S. economy.

180 million Americans visit estuary and coastal waters each year for recreation and tourism.

Commercial and recreational fishing employ 1.5 million people and contribute $111 billion to the nation's economy

What an Estuary Looks Like

One single estuary can include a wide variety of habitat types. The types of habitats are usually determined by the local geology and climate. Habitats associated with estuaries include salt marshes, mangrove forests, mud flats, tidal streams, rocky intertidal shores, reefs, and barrier beaches.

Examples of nearly every type of estuarine habitat exist along the coastline of the United States.

Also along the Texas coast—barrier islands protect estuaries that have formed narrow lagoons with small openings to the Gulf of Mexico. In these areas, estuaries with very little freshwater input often become “hypersaline” or super salty.

Northern California and Alaska—coastal rivers flow quickly out of the mountains and into very small estuaries.

Threats to Estuaries

Estuaries are fragile ecosystems that are very susceptible to natural and man-made disturbances. Natural disturbances are caused by the forces of nature such as winds, tidal currents, waves, and ice and disruptive human activities can include coastal settlement, land clearance, pollution, poor farming practices, and overfishing.

The greatest threat to estuaries is, by far, their large-scale conversion by draining, filling, damming, or dredging. These activities result in the immediate destruction and loss of estuarine habitats. Until the last few decades, many estuary habitats in North America were drained and converted into agricultural areas; others were filled to create shipping ports and expand urban areas.

In the United States, 38 percent of the wetlands associated with coastal areas have been lost to these types of activities. In some areas, the estuarine habitat loss is as high as 60 percent.

Our Work in Estuaries

We restore habitat in estuaries all across the country. In 2010, we replaced culverts on Bride Brook in Connecticut, which is part of the Long Island Sound estuary. With the increased flow from the new, larger culvert, fish were able to swim upstream for the first time in more than a decade. And this year, Bride Brook reaped the benefits: this year’s run was more than triple what we had seen in the past.

Protecting and Restoring America’s Largest Estuary

The Chesapeake Bay is North America’s largest estuary. The Chesapeake Bay watershed—the area from which water drains into the Bay—encompasses more than 64,000 square miles in six states (Delaware, Maryland New York, Pennsylvania, Virginia, West Virginia) and all of Washington, D.C. Roughly 17 million people live in the Chesapeake Bay watershed, and their day-to-day actions affect the health of this important resource.